The present invention relates to the use of sphingomyelinase to increase the levels of skin and mucosal ceramides, and dermatological and cosmetic compositions suitable for topical application containing same.
Ceramide (N-acylsphingosine) is a lipid metabolite which has recently been proposed as an important intracellular messenger released inside the cell within a few hours of stimulation with various agents or as a result of serum deprivation, and is related to cell blockade in the G0/G1 phase and apoptosis. Ceramide is currently regarded as a second messenger in the context of the sphingomyelin signal transduction pathway. It is released by sphingomyelin as a result of the effect of sphingomyelinases, which are forms of phospholipase C specific for sphingomyelin. Inside the cells, ceramide can influence growth and differentiation, regulate protein secretion, induce DNA fragmentation and apoptosis, and increase the synthesis and secretion of cytokines. The molecular mechanisms underlying these various different actions are as yet not entirely known. More is known, on the other hand, about extracellular agonists which cause the release of ceramide. Hydrolysis of sphingomyelin occurs rapidly after exposure of the cells to exogenous sphingomyelinase or to agonists which activate endogenous sphingomyelinases. Such agonists include TNF-xcex1, Fas ligand, interleukin 1-xcex2, IFN-xcex3, 1xcex1, 25-dihydroxyvitamin D3 and NGF.
Sfingomyelinase-containing cosmetic compositions are already known. Japanese Patent Publication 63 216813 discloses such a composition wherein the sphingomyelinase obtained therein aims at counteracting the physiological decrease of this enzyme in aging skin, thus promoting the conversion of sphingomyelin to ceramide which, in turn, brings about a beneficial moisturising effect on the skin.
The Japanese publication, however, does not disclose or in the least suggest that these compositions might be used therapeutically for treating dermatological disorders. Moreover, sphingomyelinase is obtained via a cumbersome and complex extraction method from tissues of higher animals, such as brain and liver.
The importance of ceramide in the skin metabolism shall be clearly apparent from what follows here below.
The main cellular constituents of the epidermis are keratinocytes, melanocytes, Langerhans cells, fibroblasts, endothelial cells and macrophages. Mono- and polymorphonuclear leukocytes can infiltrate the skin in the course of inflammation or tumours. The intracellular sp ace, on the other hand, consists mainly of neutral lipids, glyco-proteins, protein degradation products, desmosomes, active enzymes, products of sebaceous glands and ceramides. As long as this xe2x80x9cbricks and mortarxe2x80x9d structure is intact, the skin is endowed with both a protective layer and a selectively permeable filter.
During the differentiation process of the epidermis, which starts with cell division in the basal layers and ends with the death of keratinocytes and the development of the lipid barrier, the cells modify their lipid synthesis capability. The result is that the basal layer of the epidermis is characterized by phospholipids and cholesterol, whereas the outermost layer is characterized by cholesterol, free fatty acids, and, above all, ceramides. The lipids of the horny layer, the main component of which consists of sphingolipids, play a crucial role in maintaining the permeability barrier of the epidermis to water. The sphingolipids a re extruded from the lamellar bodies of the granular cells of the epidermis. Ceramides (sphingolipids), which make up 43-46% of the horny layer, are the main polar lipids of the horny layer and play a fundamental role in the barrier function of the skin against water leakage in cell adhesion and in the differentiation of the epidermis. Literature data indicate that ceramides are synthesised de novo in the epidermis via phospholipid-like intermediates. They are present in fairly high concentrations in the horny layer (up to 40% of total lipids).
Like the appearance of the surface of the skin, its functional properties also undergo changes with ageing. Ageing skin is characterized by a reduced water content in the horny layer associated with reduced transdermal leakage of water. It has been shown that the ceramide 2:sphingolipid ratio decreases with age. The drop in ceramide associated with ageing may be responsible for the dehydration of the skin which is observed in the course of ageing.
In addition, abnormal ceramide levels (deficiencies) have been detected in atopic eczema, dermatosis and dermatitis, in particular atopic dermatitis, and psoriasis. Recently, an inborn deficiency of ceramide 1 has been found in autosomal recessive sphingolipidosis. Equally well known are generalised forms of sphingolipidosis such as Fabry""s disease, Gaucher""s disease and Tay-Sachs disease. Sjxc3x6gren-Larsson syndrome is associated with a deficiency of ceramide 1 and 6 with attendant destruction of the normal skin barrier.
In the light of the foregoing, it is obviously useful to maintain high levels of ceramide in the skin. It will additionally be understood that the use of sphingomyelinase proves advantageous also at mucosal level.
There are currently available on the market numerous products containing ceramides obtained by extraction methods or synthesis and used in dermatology and cosmetics. The topical external application of ceramides is proposed for remodelling the cutaneous lipid barrier altered by ageing, drugs, detergents, physical agents, etc. Such exogenous administration does not allow for the possibility that there may be qualitative and/or quantitative variations in ceramide due to age and anatomical site, seasonal factors and diseases. Clearly, then, the exogenous administration of ceramide acts only in an additive sense (endogenous+exogenous ceramide) and not in a modulatory sense (variations in ceramide according to season, anatomical site, possible disease processes in progress, etc.).
Surprisingly, we have now found that h levels of neutral, but not acid, sphingomyelinase are present in bacterial cell.
Consequently, one object of the present invention is to provide for the use of sphingomyelinase obtained from bacteria to produce dermatological or cosmetic compositions suitable for topical application in order to increase the level of ceramides in the skin and mucosa.